Method for manufacturing a multidomain liquid crystal display panel

ABSTRACT

A method for manufacturing a multidomain liquid crystal display panel, including the steps of forming a photo-alignment layer on a substrate, positioning a mask having a plurality of regions with different photo-transmittances; and forming different alignment directions in different domains of the photo-alignment layer corresponding to each of the plurality of regions by irradiating the photo-alignment layer with light through the mask.

[0001] This application claims the benefit of Korean patent applicationNo. 1997-45950, filed Sep. 5, 1997, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a liquid crystal display panel,and more particularly, to a method for manufacturing a multidomainliquid crystal display panel.

[0004] 2. Discussion of the Related Art

[0005] Generally, a liquid crystal of a liquid crystal display (LCD)panel includes anisotropic molecules. The average direction of themolecules' long axes is referred to as a director. The directordistribution in the liquid crystal is determined by an anchoring energyof the liquid crystal on a substrate, and is characterized by anorientation of the director corresponding to a minimum of a surfaceenergy of the liquid crystal and the anchoring energy. Reorientation ofthe director is achieved by applying an external electric field to theliquid crystal.

[0006] A basic unit of an LCD panel includes two glass substrates withthe liquid crystal positioned between them. To obtain uniform brightnessand a high contrast ratio in the LCD panel, it is necessary tohomogeneously align the liquid crystal in a liquid crystal cell.

[0007] The most common technique for achieving homogeneous alignmentincludes forming microgrooves on a surface of a s polymer. This resultsin a strong anchoring energy that provides a stable liquid crystalalignment. This technique is called a rubbing method, which is a simplemethod of rubbing a polymer-coated substrate with a cloth. The rubbingmethod is widely used, since it is fast and allows for large scalemanufacturing.

[0008] The rubbing method, however, has several serious drawbacks.Because the shape of the microgrooves formed on the alignment layerdepends on the rubbing cloth and a rubbing intensity, the alignment ofthe liquid crystal is often heterogeneous, causing phase distortion andlight scattering. Further, electrostatic discharge (ESD) due to rubbingof a polymer surface generates dust contamination in an active matrixLCD panel, decreasing production yield and damaging the substrate.

[0009] In order to solve these problems, a photo-alignment method hasbeen proposed using polarized ultraviolet light irradiated onto aphotosensitive polymer (M. Schadt et al., Jpn. J. Appl. Phys., 31 (1992)2155 ; T. Ya. Marusii & Yu. A. Reznikov, Mol. Mat., 3 (1993) 161). Thealignment capability of a photosensitive polymer is determined by ananisotropy of the photosensitive polymer, which is induced byultraviolet light irradiation.

[0010] Photo-alignment materials used in the LCD panels includepolyvinylcinnamate (PVCN) (M. Schadt et al., Jpn. J. Appl. Phys., 31(1992) 2155), polysiloxane (PS), polyimide (PI), and the like. Thephoto-alignment properties of these materials appear after theultraviolet light irradiation by a polarized light.

[0011] Moreover, these materials may be used on a base of a siliconpolyimide copolymer doped with a diazodiamine dye, or on a base of apolymerizable nematic liquid crystal monomer composition for opticalstorage (W. M. Gibbons et al., Nature, 351 (1991) 49 ; P. J. Shannon etal., Nature, 368 (1994) 532). These materials are photosensitive in avisible spectrum.

[0012] While the alignment direction of the alignment layer is usuallyperpendicular to a polarization direction of the ultraviolet light usedfor irradiation, some materials provide an alignment direction parallelto the polarization direction of the ultraviolet light.

[0013] The photo-alignment method has various advantages over theconventional rubbing method. First, there is no electrostatic dischargefrom a rubbing cloth in rubbing, and therefore, the dust particles donot contaminate the substrate. Second, the photosensitive polymer isable to control the alignment direction and azimuthal anchoring energyof the alignment layer. This, therefore, determines alignment directionin the liquid crystal cefl. The photo-alignment method is therefore usedto form a multidomain liquid crystal cell, which improves the viewingangle characteristics of the LCD panel.

[0014] Several methods are known for forming the multidomain liquidcrystal cell using the photo-alignment method.

[0015] A method proposed by W. M. Gibbons et al. (Nature, 351 (1991) 49)suggests that after rubbing a photosensitive polymer-coated substrateunidirectionally, the substrate may be irradiated by the ultravioletlight to form an alignment direction perpendicular to the rubbingdirection. The LCD panel includes a first substrate, a second substraterubbed in the same direction as the rubbing direction of the firstsubstrate, and a liquid crystal between the first and second substrates.In the Gibbons method, however, it is necessary to use the rubbingmethod to make microgrooves in the alignment layer, which still causesproblems with the electrostatic discharge and the dust contaminationfrom rubbing.

[0016] Modification of the Gibbons method is proposed by P. J. Shannonet al. (Nature, 368 (1994) 532). In the Shannon method, instead ofrubbing the alignment layer, the first alignment is performed byirradiating the alignment layer with polarized light. While the Shannonmethod overcomes the disadvantages of the rubbing method, it has aproblem in that in order to change the alignment direction during themanufacturing process, two separate irradiation steps using polarizedlight are required, with the polarization directions being mutuallyperpendicular. Several processing steps are therefore needed.

SUMMARY OF THE INVENTION

[0017] Accordingly, the present invention is directed to a method formanufacturing a multidomain liquid crystal display panel thatsubstantially obviates one or more of problems due to limitations anddisadvantages of the related art.

[0018] An object of the present invention is to provide a method formanufacturing a multidomain liquid crystal display panel with a singleirradiation step by ultraviolet light and visible light.

[0019] Additional features and advantages of the present invention willbe set forth in the description which follows, and will be apparent fromthe description, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure and process particularly pointed out in thewritten description as well as in the appended claims.

[0020] To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, inaccordance with a first aspect of the present invention there isprovided a method for manufacturing a multidomain liquid crystal displaypanel, including the steps of forming a photo-alignment layer on asubstrate, positioning a mask having a plurality of regions withdifferent photo-transmittances, and forming different alignmentdirections in different domains of the photo-alignment layercorresponding to each of the plurality of regions by irradiating thephoto-alignment layer with light through the mask.

[0021] In another aspect of the present invention there is provided amultidomain liquid crystal display panel, including a first substrateand a second substrate, a liquid crystal positioned between the firstsubstrate and the second substrate, and a photosensitive layer coveringthe first substrate and having a plurality of first domains and aplurality of second domains, wherein an alignment of photosensitivemolecules in the plurality of first domains is orthogonal to alignmentof photosensitive molecules in the plurality of second domains, whereinthe photosensitive layer includes an ultraviolet light sensitivematerial and a visible light sensitive material.

[0022] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

[0023] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention that together with the description serve to explain theprinciples of the invention.

[0024] In the drawings:

[0025]FIG. 1 shows a formula of an alignment layer material PSCN-1according to a first embodiment of the present invention;

[0026]FIG. 2 shows a formula of an alignment layer material AB(azobenzene) according to the first embodiment of the present invention;

[0027]FIG. 3 shows a formula of an alignment layer material PSCN-2according to second and third embodiments of the present invention;

[0028]FIG. 4 shows a formula of an alignment layer material methylorangeaccording to the second embodiment of the present invention;

[0029]FIG. 5 shows a formula of an alignment layer material methylredaccording to the third embodiment of the present invention.

[0030]FIG. 6 shows an experimental setup for forming a multidomainalignment direction on the alignment layer according to the presentinvention.

[0031]FIG. 7 shows an absorption spectrum of a mixture of the PSCN-1 andAB polymers;

[0032]FIG. 8 shows an irradiation spectrum of an Hg lamp;

[0033]FIG. 9 shows an absorption spectrum of the PSCN-2 polymer dopedwith an azo dye methylorange; and

[0034]FIG. 10 shows an absorption spectrum of the PSCN-2 polymer dopedwith an azo dye methylred.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings.

[0036] Generally, it is known in the art that photosensitive materialsprovide an alignment direction of an alignment layer that is eitherhorizontal or vertical relative to a polarization direction ofultraviolet light used for irradiation. Also, the alignment direction ofthe alignment layer is determined by a spectrum distribution of thelight used to irradiate the alignment layer. That is, the alignmentdirection is determined by a chemical structure change of the alignmentmaterial due to visible light and ultraviolet light irradiation.

[0037] For example, when a PSCN-1 polymer, shown in FIG. 1, isirradiated by 260 nm ultraviolet light of intensity 2-5 mW/cm² for 5minutes, an alignment direction that is horizontal relative to apolarization direction of the ultraviolet light is created. Also, if aPSCN-2 polymer, shown in FIG. 3, is irradiated under the same conditionsfor 30 minutes, the PSCN-2 polymer exhibits similar properties. Thesematerials absorb light in a wavelength range of 200-400 nm. In thePSCN-1 and PSCN-2 as above, the end groups of the siloxane, —OSi(CH₃)₃,are substituted with other functional groups, such as OH, and the like.And the repeat unit n in the FIGS. 1, 2, and 3 is 1 to 40, andpreferably is 32.

[0038] Furthermore, polymers absorbing light in a visible spectrumexhibit good photo-alignment properties. For instance, AB (azobenzene),shown in FIG. 2, absorbs light in a wavelength range of 400-500 nm andhas a photo-induced alignment direction that is vertical relative to thepolarization direction of the irradiating light.

[0039] This result can also be obtained by doping a low-molecular-weightanisotropic dye into the photosensitve polymer. For example, ifpolysiloxane and polyimide doped with a diazodiamine dye and azo dyemolecules are irradiated by a polarized visible light, an alignmentdirection that is vertical to the polarization direction of the visiblelight is created (W. M. Gibbons et al., Nature, 351 (1991) 49 ; Y.Iimura et al., Jpn. J. Appl. Phys. 32 (1993) L93 ; A. Dyadyusha et al.,Mol. Mater. 5 (1995) 183).

[0040] Moreover, if the PSCN-1 and PSCN-2 polymers doped with azo dyesmethylorange (shown in FIG. 4) and methylred (shown in FIG. 5) areirradiated by a polarized light in their absorption bands, whichcorrespond to a transmission region of the PSCN-1 and PSCN-2 polymers,an alignment direction that is horizontal relative to the polarizationdirection of the irradiating light is created.

[0041] These results motivate a new method to achieve multidomain liquidcrystal alignment in an LCD panel. The present invention uses the abovephoto-alignment properties to control the alignment direction of thealignment layer by a single photo-irradiation step the alignment layerincludes a combination of materials that possess different absorptionbands and result in mutually orthogonal alignment directions dependingon the wavelength of the irradiating light.

[0042] A method for manufacturing the multidomain LCD panel of thepresent invention uses irradiation of different regions of the substrate(here, Δλ_(|) region and Δλ_(⊥) region), such that liquid crystalalignment is formed in orthogonal directions. Δλ_(|) light is lightirradiating the Δλ_(|) region that induces liquid crystal to alignhorizontally to the polarization direction of irradiated light, andΔλ_(|) light is light of irradiating the Δλ_(⊥) region that induces theliquid crystal to align vertically to polarized direction of irradiatedlight. As a result, domains of the alignment layer so irradiated arealigned to have mutually orthogonal directions. A substrate having thephoto-alignment layer so irradiated can then be used for manufacturingthe multidomain LCD panel.

[0043] An experimental setup for forming the multidomain alignmentdirection of the alignment layer is shown in FIG. 6. A substrate iscovered with a photo-alignment material PM. The irradiating lightincludes Δλ_(|) light and Δλ_(⊥) light emitted by a mercury (Hg) lamp.The photo-alignment material PM includes a mixture that results inmutually orthogonal alignment directions after irradiating, therebyforming the photo-alignment layer. The irradiated light passes through apolarizer P that linearly polarizes the light, a condenser C, and a maskM.

[0044] The mask M includes two types of regions. The first region (T₁)passes Δλ_(|) light, but not Δλ_(⊥) light. The second region (T₂) passesΔλ_(⊥) light, but not Δλ_(|) light. As a result of the irradiating, aphoto-alignment region corresponding to the first region (T₁) has analignment direction that is horizontal relative to the irradiatinglight, and a photo-alignment region corresponding to the second region(T₂) has as alignment direction that is vertical relative to theirradiating light.

[0045] In the multidomain LCD panel of the present invention, a pixel isformed with the alignment directions of each domain being mutuallyorthogonal. For example, it is possible to fabricate a cell with a firstsubstrate having the alignment layer photo-irradiated and the secondsubstrate having the alignment layer aligned unidirectionally. Thealignment layers are placed so that the alignment direction of theunidirectional alignment layer coincides with one of the alignmentdirections of photo-alignment layer. The liquid crystal then alignshomogeneously in a region where the alignment directions of bothsubstrates are parallel, and is twisted in a region where the alignmentdirections of both substrates are mutually orthogonal. If the liquidcrystal cell is placed between a parallel and a crossed polarizer, it ispossible to control brightness and darkness in the LCD panel.

[0046] The present invention allows manufacturing of a multidomain LCDpanel having a wide viewing angle. The LCD panel has a twistedtwo-domain construction where the liquid crystal alignment of eachdomain is rotated 90° relative to a neighboring domain. Each domain hasan asymmetric viewing angle, but when it is compensated by a sum ofviewing angles of-both domains, the viewing angle becomes symmetric.

[0047] In the first preferred embodiment, a solution of the PSCN-1polymer and the AB polymer (weight ratio 2:1) in 1,2-dichloroethane isprepared. Total polymer concentration in the solution is 10 g/l. Thepolymers are coated onto a glass substrate by a spin-coating method for30 seconds.

[0048] The rotation speed of a spin-coating machine is 4000 rev/minute.The substrate is treated by soft baking after centrifugal separation at60° C. for 1 hour. Absorption spectrum of the polymers is shown in FIG.7. The PSCN-1 polymer absorbs ultraviolet light, and the AB polymerabsorbs the visible light.

[0049] The substrate is prepared by an experimental setup as shown inFIG. 6. The Hg lamp is a source of both the ultraviolet light and thevisible light. The polarization direction of the ultraviolet light isparallel to a long side of the glass substrate. Emission spectrum of theHg lamp is shown in FIG. 8. The emission spectrum is measured on MDR-12with FhotoMult FEU-79 at P=250 W. Light intensity at the mask M is 3mW/cm². The mask is a thin glass substrate 2×3 cm², with pieces of apolymer film 1×1 mm² in a lattice arrangement positioned on its surface.The polymer film blocks the ultraviolet light but passes the visiblelight emitted by the Hg lamp (see FIG. 8). The substrate is irradiatedfor 15 minutes.

[0050] The liquid crystal cell includes the first substrate formed withthe alignment layer and the second glass substrate coated with apolyimide CU-2012 and rubbed. The alignment layer has unidirectionalalignment parallel to the long side of the substrate, and the liquidcrystal cell is then fabricated using conventional methods. The cell gapis 0.5 mm and is filled with a liquid crystal ZLI 4801-000 at a roomtemperature. The liquid crystal cell is placed between crossedpolarizers.

[0051] In a second preferred embodiment, similar to the first preferredembodiment, a mixture of the PSCN-2 polymer and methylorange is used asa photo-alignment layer. Weight concentration of methylorange in thePSCN-2 polymer is 20%. The irradiation of a substrate is carried out for5 minutes and results similar to the first preferred embodiment areobtained. An absorption spectrum of the photo-alignment material of thesecond preferred embodiment is shown in FIG. 9.

[0052] In a third preferred embodiment, similar to the first preferredembodiment, a mixture of the PSCN-2 polymer and methylred is used as thephoto-alignment layer. Weight concentration of methylred in the PSCN-2polymer is 30%. A substrate coated with the mixture is irradiated for 30minutes, with results similar to the first preferred embodiment.Absorption spectrum of the mixture of the PSCN-2 polymer and methylredis shown in FIG. 10.

[0053] A method for manufacturing the multidomain LCD panel of thepresent invention is described using an alignment layer that includesmaterials having different absorption bands and results in mutuallyorthogonal alignment directions after irradiation by light of differentwavelength regions. Therefore, only a single photo-irradiation step isrequired for a mask having a plurality of regions with different lighttransmission properties. Furthermore, the multidomain LCD panel has goodwide viewing angle characteristics, and can also be used for opticalinformation storage devices.

[0054] While the invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for manufacturing a multidomain liquidcrystal display panel, comprising the steps of: forming aphoto-alignment layer on a substrate; positioning a mask having aplurality of regions with different photo-transmittances; and formingdifferent alignment directions in different domains of thephoto-alignment layer corresponding to each of the plurality of regionsby irradiating the photo-alignment layer with light through the mask. 2.The method of claim 1, wherein the photo-alignment layer includes aplurality of materials corresponding to a first region and a secondregion of the mask.
 3. The method of claim 2, wherein an alignmentdirection of domains corresponding to the first region of the mask ishorizontal relative to a polarization direction of irradiating light,and an alignment direction of domains corresponding to the second regionof the mask is vertical relative to the polarization direction of theirradiating light.
 4. The method of claim 2, wherein domainscorresponding to the first region of the mask include a PSCN derivative,and domains corresponding to the second region of the mask include anazobenzene derivative.
 5. The method of claim 2, wherein domainscorresponding to the first region of the mask include a PSCN derivative,and domains corresponding to the second region of the mask includemethylorange.
 6. The method of claim 2, wherein domains corresponding tothe first region of the mask include a PSCN derivative, and domainscorresponding to the second region of the mask include methyl red. 7.The method of claim 1, wherein each of the plurality of regions of themask has a first region and a second region, wherein the first andsecond regions transmit light in a different wavelength range.
 8. Themethod of claim 7, wherein the first region transmits ultraviolet light.9. The method of claim 7, wherein the second region transmits visiblelight.
 10. The method of claim 1, wherein a single exposure is used toirradiate the photo-alignment layer.
 11. The method of claim 1, whereinthe photo-alignment layer includes a mixture of photosensitive materialsphotoreacting to light of different wavelength ranges.
 12. A multidomainliquid crystal display panel, comprising: a first substrate and a secondsubstrate; a liquid crystal positioned between the first substrate andthe second substrate; and a photosensitive layer covering the firstsubstrate and having a plurality of first domains and a plurality ofsecond domains, wherein an alignment of photosensitive molecules in theplurality of first domains is orthogonal to alignment of photosensitivemolecules in the plurality of second domains; wherein the photosensitivelayer includes an ultraviolet light sensitive material and a visiblelight sensitive material.
 13. The multidomain liquid crystal displaypanel of claim 12, wherein the ultraviolet light sensitive materialincludes at least one of PSCN-1 and PSCN2.
 14. The multidomain liquidcrystal display panel of claim 12, wherein the visible light sensitivematerial includes at least one of methylorange and methylred.
 15. Themultidomain liquid crystal display panel of claim 12, wherein thephotosensitive layer includes a mixture of PSCN-1 polymer and an ABpolymer.
 16. The multidomain liquid crystal display panel of claim 15,wherein the second substrate further includes a layer of polyimide and aplurality of microgrooves.
 17. The multidomain liquid crystal displaypanel of claim 12, wherein the photosensitive layer includes a mixtureof PSCN-2 polymer and 20% methylorange.
 18. The multidomain liquidcrystal display panel of claim 12, wherein the photosensitive layerincludes a mixture of PSCN-2 polymer and 30% methylred.
 19. Themultidomain liquid crystal display panel of claim 12, wherein thephotosensitive layer is exposed to ultraviolet and visible light using asingle exposure.
 20. The multidomain liquid crystal display panel ofclaim 12, wherein an absorption band of the visible light sensitivematerial is in a transmission band of the ultraviolet light sensitivematerial.